Study on the Structure of Peroxide Cross-Linked Polyethylene Pipes with Several Stabilizers

Cross-linked polyethylene (PEX) pipes used in hot water supply are required for high mechanical strength and high creep resistance at high temperature.Especially PEX-a pipes which are made by peroxide cross-linking have better performance, such as creep resistance and thermal shock resistance than the pipes made by the other cross-linking method.Because the PEX-a pipes indicate the higher cross-link degree as compared with the other PEX pipes.In this study, the PEX-a pipes which were mixed with several stabilizers were tested to evaluate the effects on cross-link degree and the oxygen induction time.And also they are evaluated with the chlorine aqueous solution by the performance of the long-term hydrostatic pressure test and the long-term hydro dynamic pressure test.As a result, it was found that the combination of antioxidants for PEX-a pipes plays an important role to prolong the oxygen induction time without inhibiting the cross-linking.From the results of the 1 H pulsed NMR measurement over the melting point of polyethylene, it was found that each peroxide PEX pipe with different antioxidant combinations indicated the different proportion and crosslink density of cross-linked region, in addition, that these pipes had the effective structure of cross-linking for the hydrostatic and hydrodynamic pressure test with the chlorine aqueous solution.Therefore, it was considered to be useful results for studies of the stricture of cross-linking of polyethylene.